This project has been undertaken to determine the effects of prolactin on the human breast and its role in human breast cancer. As a model for humans, rhesus monkeys and other subhuman primates are being used. We have determined that prolactin has a lactogenic effect on all normal mammary tissues tested. We measure alpha-lactalbumin production in response to prolactin stimulation in an organ culture system. This year we extended our observations and found that human growth hormone is a more potent lactogen than ovine prolactin in these subhuman primate mammary tissues. This brings up the possibility that growth hormone may have important physiologic effects on the breast, under normal circumstances and perhaps in breast cancer. In addition, we have found that the mammary content of alpha-lactalbumin can be significantly reduced to virutally absent levels with treatment with the prolactin lowering ergot drug pergolide mesylate. No effect on mitogenesis has been demonstrated as yet. A significant number of human breast cancers have alpha-lactalbumin in them, and our goal is to use this milk protein as a marker for prolactin activity so that we might determine the effect of prolactin in breast cancer.